There is a continuing need to improve the efficiency of water heaters. One such need is to control the cold water introduce in the water holding tank of the water heater, usually in the bottom region of the tank. When cold water is introduced in the tank it immediately mixes with the hot water resulting in a temperature drop of the hot water and prematurely lowering the temperature below the set point and triggering a demand for the heating source to heat the water, resulting in energy use. It is therefore desirable to control the flow of the cold water introduced in the tank and this applies to both electric and condensing water heaters.
With respect to condensing water heaters, it would be desirable to heat the cold water as it is introduced in the lower region of the tank before it is released in the upper hotter region of the tank. Still further, it would also be desirable to use the cold water introduce in the bottom region of the tank to further cool the hot gases released in the flue and at the same time use the heated cool water.
Known means of increasing the efficiency of flue heat recovery in condensing water heaters, is to use external heat exchange devices through which the flue gases are convected in heat exchange relationship with water which is heated thereby and used for a variety of other purposes. It is desirable to reduce the flue gases typically below 130 degrees Fahrenheit before releasing the gas vapours to atmosphere. More recently, new flue designs have been proposed where the primary central flue is connected to a secondary flue which is disposed inside the water tank for subjecting the hot gases to a second heat exchange pass with the water contained in the tank before being convected to atmosphere. Such designs results in increase costs and has added to the size of the water heater including additional external components.